U.S. patent application number 17/752213 was filed with the patent office on 2022-09-08 for light emitting diodes with reflective sidewalls comprising porous particles.
This patent application is currently assigned to Lumileds LLC. The applicant listed for this patent is LUMILEDS LLC. Invention is credited to Marcel Rene BOHMER, Kentaro SHIMIZU.
Application Number | 20220285594 17/752213 |
Document ID | / |
Family ID | 1000006418533 |
Filed Date | 2022-09-08 |
United States Patent
Application |
20220285594 |
Kind Code |
A1 |
BOHMER; Marcel Rene ; et
al. |
September 8, 2022 |
LIGHT EMITTING DIODES WITH REFLECTIVE SIDEWALLS COMPRISING POROUS
PARTICLES
Abstract
Sidewall reflectors disposed on the sidewalls of an LED or pcLED
comprise porous (for example, hollow) high refractive index light
scattering particles dispersed in a transparent binder. The porous
particles exhibit a high refractive index contrast and
corresponding strong scattering at the interfaces between the
porous particle material and one or more pores in each particle.
These sidewall reflectors can provide light confinement with thin
reflector structures, allowing close spacing between LEDs and
pcLEDs, and may be advantageously employed in microLED arrays.
Inventors: |
BOHMER; Marcel Rene;
(Eindhoven, NL) ; SHIMIZU; Kentaro; (Sunnyvale,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LUMILEDS LLC |
San Jose |
CA |
US |
|
|
Assignee: |
Lumileds LLC
San Jose
CA
|
Family ID: |
1000006418533 |
Appl. No.: |
17/752213 |
Filed: |
May 24, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/US20/64318 |
Dec 10, 2020 |
|
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17752213 |
|
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16712607 |
Dec 12, 2019 |
11189757 |
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PCT/US20/64318 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 33/60 20130101;
H01L 33/52 20130101; H01L 27/156 20130101 |
International
Class: |
H01L 33/60 20060101
H01L033/60; H01L 33/52 20060101 H01L033/52; H01L 27/15 20060101
H01L027/15 |
Claims
1. A light emitting device comprising: a substrate; a semiconductor
light emitting diode disposed on the substrate, the semiconductor
diode comprising a top surface, an oppositely positioned bottom
surface adjacent the substrate, and sidewalls connecting the top
and bottom surfaces of the semiconductor diode, the semiconductor
diode having non-zero transverse dimensions less than about 1.0 mm;
a wavelength converting structure comprising a top light output
surface, an oppositely positioned bottom surface adjacent the top
surface of the semiconductor light emitting diode, and side walls
connecting the top and bottom surfaces of the wavelength converting
structure; and reflectors disposed on only the sidewalls of the
wavelength converting structure and on only the sidewalls of the
semiconductor light emitting diode, the reflectors comprising
porous light scattering particles dispersed in a transparent
binder, the porous light scattering particles each including
therein one or more pores defined by inner surfaces of the porous
light scattering particles, the reflectors substantially preventing
transmission of light exiting the light emitting device through the
side walls of the semiconductor diode or through the side walls of
the wavelength converting structure.
2. The light emitting device of claim 1, the semiconductor diode
having non-zero transverse dimensions less than about 0.2 mm.
3. The light emitting device of claim 1, wherein (i) at least some
of the porous light scattering particles include therein one or
more gas-filled pores, or (ii) at least some of the porous light
scattering particles include therein one or more evacuated
pores.
4. The light emitting device of claim 1, wherein at least some of
the porous light scattering particles include therein one or more
closed pores.
5. The light emitting device of claim 1, wherein at least some of
the porous light scattering particles include therein one or more
open pores.
6. The light emitting device of claim 1, wherein the porous light
scattering particles have a refractive index of greater than or
equal to about 2.0 and the pores have a refractive index of about
1.0.
7. The light emitting device of claim 1, wherein (i) the porous
light scattering particles have transverse sizes of about 0.3
microns to about 10. microns, or (ii) the pores have transverse
sizes of about 0.10 microns to about 0.5 microns.
8. The light emitting device of claim 1, wherein the porous light
scattering particles have a bimodal size distribution with a first
peak at a first transverse size and a second peak at about one
fourth or less of the first transverse size.
9. The light emitting device of claim 1, wherein at least some of
the porous light scattering particles include a hydrophobic
coating.
10. The light emitting device of claim 9, wherein the hydrophobic
coating coats internal surfaces of at least some of the pores in
the porous light scattering particles.
11. A light emitting device comprising: a plurality of phosphor
converted light emitting diodes disposed on a shared substrate with
adjacent pairs of the phosphor converted light emitting diodes
separated by corresponding gaps, each phosphor converted light
emitting diode having non-zero transverse dimensions less than
about 1.0 mm, each gap having a non-zero width less than about 0.1
mm; and a light scattering composition filling only the gaps to
form corresponding sidewall reflectors shared by corresponding
adjacent pairs of the phosphor converted light emitting diodes, the
light scattering composition comprising porous light scattering
particles dispersed in a transparent binder, the porous light
scattering particles each including one or more pores defined by
inner surfaces of the porous light scattering particles, the
sidewall reflectors substantially preventing transmission of light
across the gaps between the corresponding adjacent pairs of the
phosphor converted light emitting diodes.
12. The light emitting device of claim 11, wherein (i) each
phosphor converted light emitting diode has non-zero transverse
dimensions less than about 0.2 mm, or (ii) each gap has a non-zero
width less than about 0.05 mm.
13. The light emitting device of claim 11, wherein (i) each
phosphor converted light emitting diode has non-zero transverse
dimensions less than about 0.10 mm, or (ii) each gap has a non-zero
width less than about 0.015 mm.
14. The light emitting device of claim 11, wherein (i) at least
some of the porous light scattering particles include therein one
or more gas-filled pores, or (ii) at least some of the porous light
scattering particles include therein one or more evacuated
pores.
15. The light emitting device of claim 11, wherein at least some of
the porous light scattering particles include therein one or more
closed pores.
16. The light emitting device of claim 11, wherein at least some of
the porous light scattering particles include therein one or more
open pores.
17. The light emitting device of claim 11, wherein the porous light
scattering particles have a refractive index of greater than or
equal to about 2.0 and the pores have a refractive index of about
1.0.
18. The light emitting device of claim 11, wherein (i) the porous
light scattering particles have transverse sizes of about 0.3
microns to about 10. microns, or (ii) the pores have transverse
sizes of about 0.10 microns to about 0.50 microns.
19. The light emitting device of claim 11, wherein at least some of
the porous light scattering particles include a hydrophobic
coating.
20. The light emitting device of claim 19, wherein the hydrophobic
coating coats internal surfaces of at least some of the pores in
the porous particle.
Description
PRIORITY CLAIM
[0001] This application is a continuation of App No
PCT/US2020/064318 entitled "Light emitting diodes with reflective
sidewalls comprising porous particles" filed 10 Dec. 2020 in the
names of Marcel Rene Bohmer and Kentaro Shimizu, which in turn
claims priority of U.S. non-provisional application Ser. No.
16/712,607 entitled "Light emitting diodes with reflective
sidewalls comprising porous particles" filed 12 Dec. 2019 in the
names of Marcel Rene Bohmer and Kentaro Shimizu (now U.S. Pat. No.
11,189,757); both of said applications are incorporated by
reference as if set forth herein in their entireties.
FIELD OF THE INVENTION
[0002] The invention relates generally to phosphor-converted light
emitting diodes.
BACKGROUND
[0003] Semiconductor light emitting diodes and laser diodes
(collectively referred to herein as "LEDs") are among the most
efficient light sources currently available. The emission spectrum
of an LED typically exhibits a single narrow peak at a wavelength
determined by the structure of the device and by the composition of
the semiconductor materials from which it is constructed. By
suitable choice of device structure and material system, LEDs may
be designed to operate at ultraviolet, visible, or infrared
wavelengths.
[0004] LEDs may be combined with one or more wavelength converting
materials (generally referred to herein as "phosphors") that absorb
light emitted by the LED and in response emit light of a longer
wavelength. For such phosphor-converted LEDs ("pcLEDs"), the
fraction of the light emitted by the LED that is absorbed by the
phosphors depends on the amount of phosphor material in the optical
path of the light emitted by the LED, for example on the
concentration of phosphor material in a phosphor layer disposed on
or around the LED and the thickness of the layer.
[0005] Phosphor-converted LEDs may be designed so that all of the
light emitted by the LED is absorbed by one or more phosphors, in
which case the emission from the pcLED is entirely from the
phosphors. In such cases the phosphor may be selected, for example,
to emit light in a narrow spectral region that is not efficiently
generated directly by an LED.
[0006] Alternatively, pcLEDs may be designed so that only a portion
of the light emitted by the LED is absorbed by the phosphors, in
which case the emission from the pcLED is a mixture of light
emitted by the LED and light emitted by the phosphors. By suitable
choice of LED, phosphors, and phosphor composition, such a pcLED
may be designed to emit, for example, white light having a desired
color temperature and desired color-rendering properties.
[0007] Multiple LEDs or pcLEDs can be formed together on a single
substrate to form an array. Such arrays can be employed to form
active illuminated displays, such as those employed in, e.g.,
smartphones and smart watches, computer or video displays,
augmented- or virtual-reality displays, or signage, or to form
adaptive illumination sources, such as those employed in, e.g.,
automotive headlights, camera flash sources, or flashlights (i.e.,
torches). An array having one or several or many individual devices
per millimeter (e.g., device pitch of about a millimeter, a few
hundred microns, or less than 100 microns, and spacing between
adjacent devices less than 100 microns or only a few tens of
microns or less) typically is referred to as a miniLED array or a
microLED array (alternatively, a pLED array). Such mini- or
microLED arrays can in many instances also include phosphor
converters as described above; such arrays can be referred to as
pc-miniLED or pc-microLED arrays.
SUMMARY
[0008] An inventive light emitting device comprises a substrate, a
semiconductor light emitting diode, a wavelength converting
structure, and reflectors. The semiconductor light emitting diode
is disposed on the substrate and includes a top surface, an
oppositely positioned bottom surface adjacent the substrate, and
sidewalls connecting the top and bottom surfaces. The wavelength
converting structure comprises a top light output surface, an
oppositely positioned bottom surface adjacent the top surface of
the semiconductor light emitting diode, and side walls connecting
the top and bottom surfaces. The reflectors are disposed on the
sidewalls of the wavelength converting structure and the
semiconductor light emitting diode, and comprise porous light
scattering particles dispersed in a transparent binder. The porous
light scattering particles each include therein one or more pores
defined by inner surfaces of the porous light scattering
particles.
[0009] Another inventive light emitting device comprises a
plurality of phosphor converted light emitting diodes and a light
scattering composition. The phosphor converted light emitting
diodes are disposed on a shared substrate, with adjacent phosphor
converted light emitting diodes separated by gaps. The light
scattering composition fills the gaps to form sidewall reflectors
shared by adjacent phosphor converted light emitting diodes. The
light scattering composition comprises porous light scattering
particles dispersed in a transparent binder. The porous light
scattering particles each include therein one or more pores defined
by inner surfaces of the porous light scattering particles.
[0010] Objects and advantages pertaining to LEDs, pcLEDs, miniLED
arrays, pc-miniLED arrays, microLED arrays, and pc-microLED arrays
may become apparent upon referring to the examples illustrated in
the drawings and disclosed in the following written description or
appended claims.
[0011] This Summary is provided to introduce a selection of
concepts in a simplified form that are further described below in
the Detailed Description. This Summary is not intended to identify
key features or essential features of the claimed subject matter,
nor is it intended to be used as an aid in determining the scope of
the claimed subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 shows a schematic cross-sectional view of an example
pcLED.
[0013] FIGS. 2A and 2B show, respectively, cross-sectional and top
schematic views of an example array of pcLEDs. FIG. 2C shows a top
schematic view of an example miniLED or microLED array and an
enlarged section of 3x3 LEDs of the array. FIG. 2D shows a
perspective view of several LEDs of an example pc-miniLED or
pc-microLED array monolithically formed on a substrate.
[0014] FIG. 3A shows a schematic cross-sectional view of an example
array of pcLEDs arranged with respect to waveguides and a
projection lens. FIG. 3B shows an arrangement similar to that of
FIG. 3A, but without the waveguides.
[0015] FIG. 4A shows a top schematic view of an example miniLED or
microLED array and an enlarged section of 3.times.3 LEDs of the
array. FIG. 4B shows a perspective view of several LEDs of an
example pc-miniLED or pc-microLED array monolithically formed on a
substrate. FIG. 4C is a side cross-sectional schematic diagram of
an example of a close-packed array of multi-colored
phosphor-converted LEDS on a monolithic die and substrate.
[0016] FIG. 5A is a schematic top view of a portion of an example
LED display in which each display pixel is a red, green, or blue
phosphor-converted LED pixel. FIG. 5B is a schematic top view of a
portion of an example LED display in which each display pixel
includes multiple phosphor-converted LED pixels (red, green, and
blue) integrated onto a single die that is bonded to a control
circuit backplane.
[0017] FIG. 6A shows a schematic top view an example electronics
board on which an array of pcLEDs may be mounted, and FIG. 6B
similarly shows an example array of pcLEDs mounted on the
electronic board of FIG. 6A.
[0018] FIG. 7A, 7B, and 7C schematically illustrate an example
process flow for forming a pcLED array comprising sidewall
reflectors as described herein.
[0019] FIG. 8A schematically illustrates an example sidewall
reflector comprising porous light scattering particles dispersed in
a binder.
[0020] FIG. 8B schematically illustrates an example porous light
scattering particle as may be employed in the sidewall reflector of
FIG. 8A.
[0021] FIG. 8C schematically illustrates an example coated porous
light scattering particle as may be employed in the sidewall
reflector of FIG. 8B
[0022] The examples depicted are shown only schematically; all
features may not be shown in full detail or in proper proportion;
for clarity certain features or structures may be exaggerated or
diminished relative to others or omitted entirely; the drawings
should not be regarded as being to scale unless explicitly
indicated as being to scale. For example, individual LEDs may be
exaggerated in their vertical dimensions or layer thicknesses
relative to their lateral extent or relative to substrate or
phosphor thicknesses. The examples shown should not be construed as
limiting the scope of the present disclosure or appended
claims.
DETAILED DESCRIPTION
[0023] The following detailed description should be read with
reference to the drawings, in which identical reference numbers
refer to like elements throughout the different figures. The
drawings, which are not necessarily to scale, depict selective
examples and are not intended to limit the scope of the invention.
The detailed description illustrates by way of example, not by way
of limitation, the principles of the invention.
[0024] FIG. 1 shows an example of an individual pcLED 100
comprising a semiconductor diode structure 102 disposed on a
substrate 104, together considered herein an "LED" or
"semiconductor LED", and a wavelength converting structure (e.g.,
phosphor layer) 106 disposed on the semiconductor LED.
Semiconductor diode structure 102 typically comprises an active
region disposed between n-type and p-type layers. Application of a
suitable forward bias across the diode structure 102 results in
emission of light from the active region. The wavelength of the
emitted light is determined by the composition and structure of the
active region.
[0025] The LED may be, for example, a III-Nitride LED that emits
blue, violet, or ultraviolet light. LEDs formed from any other
suitable material system and that emit any other suitable
wavelength of light may also be used. Suitable material systems may
include, for example, various III-Nitride materials, various
III-Phosphide materials, various III-Arsenide materials, and
various II-VI materials.
[0026] Any suitable phosphor materials may be used for or
incorporated into the wavelength converting structure 106,
depending on the desired optical output from the pcLED.
[0027] FIGS. 2A-2B show, respectively, cross-sectional and top
views of an array 200 of pcLEDs 100, each including a phosphor
pixel 106, disposed on a substrate 204. Such an array may include
any suitable number of pcLEDs arranged in any suitable manner. In
the illustrated example the array is depicted as formed
monolithically on a shared substrate, but alternatively an array of
pcLEDs may be formed from separate individual pcLEDs. Substrate 204
may optionally include electrical traces or interconnects, or CMOS
or other circuitry for driving the LED, and may be formed from any
suitable materials.
[0028] Individual pcLEDs 100 may optionally incorporate or be
arranged in combination with a lens or other optical element
located adjacent to or disposed on the phosphor layer. Such an
optical element, not shown in the figures, may be referred to as a
"primary optical element". In addition, as shown in FIGS. 3A and
3B, a pcLED array 200 (for example, mounted on an electronics
board) may be arranged in combination with secondary optical
elements such as waveguides, lenses, or both for use in an intended
application. In FIG. 3A, light emitted by each pcLED 100 of the
array 200 is collected by a corresponding waveguide 192 and
directed to a projection lens 294. Projection lens 294 may be a
Fresnel lens, for example. This arrangement may be suitable for
use, for example, in automobile headlights. In FIG. 3B, light
emitted by pcLEDs of the array 200 is collected directly by
projection lens 294 without use of intervening waveguides. This
arrangement may particularly be suitable when pcLEDs can be spaced
sufficiently close to each other, and may also be used in
automobile headlights as well as in camera flash applications. A
miniLED or microLED display application may use similar optical
arrangements to those depicted in FIGS. 3A and 3B, for example.
Generally, any suitable arrangement of optical elements may be used
in combination with the pcLEDs described herein, depending on the
desired application.
[0029] Although FIGS. 2A and 2B show a 3.times.3 array of nine
pcLEDs, such arrays may include for example on the order of
10.sup.1, 10.sup.2, 10.sup.3, 10.sup.4, or more LEDs, e.g., as
illustrated schematically in FIG. 4A. Individual LEDs 100 (i.e.,
pixels) may have widths wi (e.g., side lengths) in the plane of the
array 200, for example, less than or equal to 1 millimeter (mm),
less than or equal to 500 microns, less than or equal to 100
microns, or less than or equal to 50 microns. LEDs 100 in the array
200 may be spaced apart from each other by streets, lanes, or
trenches 230 having a width w.sub.2 in the plane of the array 200
of, for example, hundreds of microns, less than or equal to 100
microns, less than or equal to 50 microns, less than or equal to 20
microns, less than or equal to 10 microns, or less than or equal to
5 microns. The pixel pitch D.sub.1 is the sum of w.sub.1 and
w.sub.2. Although the illustrated examples show rectangular pixels
arranged in a symmetric matrix, the pixels and the array may have
any suitable shape or arrangement, whether symmetric or asymmetric.
Multiple separate arrays of LEDs can be combined in any suitable
arrangement in any applicable format to form a larger combined
array or display.
[0030] LEDs having dimensions wi in the plane of the array (e.g.,
side lengths) of less than or equal to about 0.10 millimeters
microns are typically referred to as microLEDs, and an array of
such microLEDs may be referred to as a microLED array. LEDs having
dimensions wi in the plane of the array (e.g., side lengths) of
between about 0.10 millimeters and about 1.0 millimeters are
typically referred to as miniLEDs, and an array of such miniLEDs
may be referred to as a miniLED array.
[0031] An array of LEDs, miniLEDs, or microLEDs, or portions of
such an array, may be formed as a segmented monolithic structure in
which individual LED pixels are electrically isolated from each
other by trenches and or insulating material. FIG. 4B shows a
perspective view of an example of such a segmented monolithic LED
array 200. Pixels in this array (i.e., individual semiconductor LED
devices 102) are separated by trenches 230 which are filled to form
n-contacts 234. The monolithic structure is grown or disposed on
the substrate 204. Each pixel includes a p-contact 236, a p-GaN
semiconductor layer 102b, an active region 102a, and an n-GaN
semiconductor layer 102c; the layers 102a/102b/102c collectively
form the semiconductor LED 102. A wavelength converter material 106
may be deposited on the semiconductor layer 102c (or other
applicable intervening layer). Passivation layers 232 may be formed
within the trenches 230 to separate at least a portion of the
n-contacts 234 from one or more layers of the semiconductor. The
n-contacts 234, other material within the trenches 230, or material
different from material within the trenches 230 may extend into the
converter material 106 to form complete or partial optical
isolation barriers 220 between the pixels.
[0032] FIG. 4C is a schematic cross-sectional view of a close
packed array 200 of multi-colored, phosphor converted LEDs 100 on a
monolithic die and substrate 204. The side view shows GaN LEDs 102
attached to the substrate 204 through metal interconnects 239
(e.g., gold-gold interconnects or solder attached to copper
micropillars) and metal interconnects 238. Phosphor pixels 106 are
positioned on or over corresponding GaN LED pixels 102. The
semiconductor LED pixels 102 or phosphor pixels 106 (often both)
can be coated on their sides with a reflective mirror or diffusive
scattering layer to form an optical isolation barrier 220. In this
example each phosphor pixel 106 is one of three different colors,
e.g., red phosphor pixels 106R, green phosphor pixels 106G, and
blue phosphor pixels 106B (still referred to generally or
collectively as phosphor pixels 106). Such an arrangement can
enable use of the LED array 200 as a color display.
[0033] The individual LEDs (pixels) in an LED array may be
individually addressable, may be addressable as part of a group or
subset of the pixels in the array, or may not be addressable. Thus,
light emitting pixel arrays are useful for any application
requiring or benefiting from fine-grained intensity, spatial, and
temporal control of light distribution. These applications may
include, but are not limited to, precise special patterning of
emitted light from pixel blocks or individual pixels, in some
instances including the formation of images as a display device.
Depending on the application, emitted light may be spectrally
distinct, adaptive over time, and/or environmentally responsive.
The light emitting pixel arrays may provide preprogrammed light
distribution in various intensity, spatial, or temporal patterns.
The emitted light may be based at least in part on received sensor
data and may be used for optical wireless communications.
Associated electronics and optics may be distinct at a pixel, pixel
block, or device level.
[0034] FIGS. 5A and 5B are examples of LED arrays 200 employed in
display applications, wherein an LED display includes a multitude
of display pixels. In some examples (e.g., as in FIG. 5A), each
display pixel comprises a single semiconductor LED pixel 102 and a
corresponding phosphor pixel 106R, 106G, or 106B of a single color
(red, green, or blue). Each display pixel only provides one of the
three colors. In some examples (e.g., as in FIG. 5B), each display
pixel includes multiple semiconductor LED pixels 102 and multiple
corresponding phosphor pixels 106 of multiple colors. In the
example shown each display pixel includes a 3.times.3 array of
semiconductor pixels 102; three of those LED pixels have red
phosphor pixels 106R, three have green phosphor pixels 106G, and
three have blue phosphor pixels 106B. Each display pixel can
therefore produce any desired color combination. In the example
shown the spatial arrangement of the different colored phosphor
pixels 106 differs among the display pixels; in some examples (not
shown) each display pixel can have the same arrangement of the
different colored phosphor pixels 106.
[0035] As shown in FIGS. 6A and 6B, a pcLED array 200 may be
mounted on an electronics board 300 comprising a power and control
module 302, a sensor module 304, and an LED attach region 306.
Power and control module 302 may receive power and control signals
from external sources and signals from sensor module 304, based on
which power and control module 302 controls operation of the LEDs.
Sensor module 304 may receive signals from any suitable sensors,
for example from temperature or light sensors. Alternatively, pcLED
array 200 may be mounted on a separate board (not shown) from the
power and control module and the sensor module.
[0036] For many uses of pcLED arrays, it is desirable to
compartmentalize the light emitted from the individual pcLEDs in
the array. That is, it is advantageous to be able to operate an
individual pcLED pixel in the array as a light source while
adjacent pcLED pixels in the array remain dark. This allows for
better control of displays or of illumination.
[0037] It is also advantageous in many applications to place the
pcLEDs in an array close together. For example, a preferred
configuration in microLEDs is to have minimal spacing between the
individual LEDs. Also, closely spacing the pcLEDs in an array used
as a camera flash light source or in an automobile headlight may
simplify the requirements on any secondary optics and improve the
illumination provided by the array.
[0038] However, if pcLEDs in an array are placed close together,
optical cross talk between adjacent pcLED pixels may occur. That
is, light emitted by a pcLED may scatter into or otherwise couple
into an adjacent pcLED and appear to originate from that other
pcLED, preventing the desired compartmentalization of light.
[0039] Conventionally, reflective sidewalls between adjacent pcLED
pixels are used to reduce cross-talk. In one conventional approach,
the reflective sidewalls are formed from high refractive index
light scattering particles dispersed in a lower refractive index
binder material. Light scattering arising from the high index
contrast at the particle/binder interfaces optically isolates
adjacent pixels from each other. Such conventional volume
scattering approaches typically require a reflector sidewall
thickness of greater than or equal to about 50 microns, for
example, to provide sufficient optical isolation of adjacent
pixels. The light scattering can be increased if the binder is
replaced by air.
[0040] However, the mechanically stability of such a system is poor
and it is prone to contamination.
[0041] In another conventional approach, reflective sidewalls are
formed from specularly reflective metal layers or specularly
reflective stacks of dielectric layers (e.g., distributed Bragg
reflectors.
[0042] In some applications, it is desirable to space pcLED pixels
with a separation of less than or equal to 50. microns, less than
or equal to 20. microns, less than or equal to 10. microns, or less
than or equal to 4 microns. In such applications, conventional
volume scattering reflective structures as described above are
thicker than desirable. Further, in such applications it is
difficult to form specularly reflective sidewalls due to the high
aspect ratios of the channels (gaps) between adjacent pixels.
[0043] As summarized above in the "summary" section, this
specification discloses LEDs and pcLEDs having reflective sidewalls
comprising porous (for example, hollow) high refractive index light
scattering particles dispersed in a transparent binder material.
The pores are filled with air or another gas, or are evacuated.
Typically, the refractive index of the light scattering particle
material is greater than or equal to about 2.0, or greater than or
equal to about 2.5, the refractive index of the binder material is
greater than or equal to about 1.4, and the refractive index of the
(e.g., air-filled) pore is about 1.0. Light scattering in these
sidewall reflectors arises mostly at the high refractive index
contrast interfaces between the porous particle material and one or
more voids in each particle, more than at the interface between the
particle and the binder material. Because the refractive index of
the pores is low (about 1.0) compared to 1.4 or more for the
binder, more light scattering can be achieved with the same
particle materials (in porous form) in the same binder.
Alternatively, a porous particle material with a lower refractive
index may be used to achieve the same amount of scattering as with
conventional non-porous particle materials. Reflective sidewalls
comprising such porous light scattering particles can provide
desirable light confinement with thin reflector structures having,
for example, a thickness of less than or equal to about 25 microns,
less than or equal to about 15 microns, less than or equal to about
10. microns, or less than or equal to about 4 microns.
[0044] The porous light scattering particles may be, for example,
porous Titanium
[0045] Oxide (TiO.sub.2) particles or porous Zirconium Oxide
(ZrO.sub.2) particles, but other materials may be used if suitable.
The particles may have diameters (or longest dimensions) of, for
example, about 0.3 microns to about 10. microns. The pores (voids)
in the particles may have diameters (or longest dimensions) of, for
example, about 0.10 microns to about 0.50 microns, about 0.10
microns to about 0.25 microns, about 0.20 microns to about 0.25
microns, or about 0.30 microns. Pores having a diameter of about
0.20 microns to about 0.25 microns may provide maximum scattering.
In some variations, porous light scattering particles have a
diameter of about 0.30 microns and each include a single closed
pore having a diameter of about 0.20 microns.
[0046] The size distribution of the light scattering particles may,
for example, be bimodal with a first peak at a large diameter and a
second peak at a diameter of at most about 1/4 of the diameter of
the first peak. This can be advantageous, with particles at the
smaller of the two diameters fitting into gaps between particles of
the larger of the two diameters.
[0047] Hollow particles, for instance hollow TiO2 particles, have
been used to enhance the light harvesting in photovoltaic
applications (Koh et al., advanced materials 2008; Yu, J. power
sources 2011; Sasanpour, J. Opt. 2011). Most experiments and
theoretical studies have concentrated on particles having a single
pore, but for use in sidewall reflectors as described herein it may
be advantageous to form larger particles with a plurality of pores,
as long as the particle size is significantly smaller than the
spacing between pcLEDs. Apart from spherical particles, cylindrical
hollow particles can be used to enhance the scattering effect
(Sasanpour et al.).
[0048] The porous particles may include open pores, closed pores,
or both open and closed pores. Open pores have a connection to the
outer surface of the particle, and thus for example to the
binder.
[0049] Porous particles comprising open pores may be coated with a
hydrophobic material that prevents binder material from flowing
into and filling or partially filling the open pores during the
deposition and curing processes by which the sidewall reflectors
are formed. The hydrophobic coating may coat internal surfaces
defining the open pores, for example. Porous particles not
comprising open pores may also be coated with a hydrophobic
material to reduce sensitivity to moisture. Suitable hydrophobic
materials may include, for example, silanes having hydrophobic
(e.g., organic) side groups such as, for example,
alkoxy-alkylsilanes, chloro-alkylsilanes, hexamethyldisilazane, and
fluorinated silanes.
[0050] The transparent binder material may be for example a
silicone or a sol-gel glass material.
[0051] An example process flow for making a pcLED array employing
such sidewall reflectors is described next with respect to FIGS.
7A-7C. Any other suitable process may be used instead. Details of
the example sidewall reflectors are described with respect to FIGS.
8A-8C.
[0052] FIG. 7A schematically illustrates in a cross-sectional view
a portion of an example pcLED array. In the array, semiconductor
light emitting diodes 502 are mounted on a substrate 504. A
wavelength converting structure 506 is located on an upper surface
of each light emitting diode 502, opposite from substrate 504, to
form a pcLED. The wavelength converting structures 506 may be
ceramic phosphor structures, phosphor particles dispersed in a
binder, or any other suitable wavelength converting structure.
Adjacent pcLED pixels are separated from each other by a street
(gap) having a width 508. Width 508 may be, for example, less than
or equal to about 50. microns, less than or equal to about 20.
microns, or less than or equal to about 10. microns, but any
suitable spacing may be used.
[0053] As shown in FIG. 7B a layer 510 of a light scattering
composition comprising porous light scattering particles dispersed
in a binder, as described above, is disposed in the streets between
the pcLEDs in contact with sidewalls of the pcLEDs, and optionally
over top surfaces of the pcLEDs. Layer 510 may be deposited by, for
example, spin coating, spray coating, over-molding, printing, or
any other suitable deposition method.
[0054] As shown in FIG. 7C, any light scattering composition
present on top surfaces of the pcLEDs is removed and the remaining
light scattering composition is cured to form reflective sidewalls
512 extending from substrate 504 to top light emitting surfaces of
the wavelength converting structures 506.
[0055] FIG. 8A schematically shows detail of an example reflective
sidewall reflector 512 comprising porous light scattering particles
604 dispersed in a binder 602. FIG. 8B schematically shows details
of an example porous light scattering particle 604, comprising one
or more voids 608 in particle material 606. FIG. 8C schematically
shows the porous light scattering particle of FIG. 8B coated with a
hydrophobic coating 610 preventing binder material 602 from
entering pores 608 during deposition and curing of the light
scattering composition. Hydrophobic coating 610 may, for example,
penetrate or partially penetrate voids 608 that open to a surface
of particle 604. Coating 610 need not form a continuous physical
barrier layer as schematically shown in FIG. 8C.
[0056] In addition to the preceding, the following example
embodiments fall within the scope of the present disclosure or
appended claims:
[0057] Example 1. A light emitting device comprising: a substrate;
a semiconductor light emitting diode disposed on the substrate, the
semiconductor diode comprising a top surface, an oppositely
positioned bottom surface adjacent the substrate, and sidewalls
connecting the top and bottom surfaces; a wavelength converting
structure comprising a top light output surface, an oppositely
positioned bottom surface adjacent the top surface of the
semiconductor light emitting diode, and side walls connecting the
top and bottom surfaces; and reflectors disposed on the sidewalls
of the wavelength converting structure and the semiconductor light
emitting diode, the reflectors comprising porous light scattering
particles dispersed in a transparent binder, the porous light
scattering particles each including therein one or more pores
defined by inner surfaces of the porous light scattering
particles.
[0058] Example 2. The light emitting device of Example 1, wherein
at least some of the porous light scattering particles include
therein one or more gas-filled pores.
[0059] Example 3. The light emitting device of any one of Examples
1 or 2, wherein at least some of the porous light scattering
particles include therein one or more evacuated pores.
[0060] Example 4. The light emitting device of any one of Examples
1 through 3, wherein at least some of the porous light scattering
particles include therein one or more closed pores.
[0061] Example 5. The light emitting device of any one of Examples
1 through 4, wherein at least some of the porous light scattering
particles include therein one or more open pores.
[0062] Example 6. The light emitting device of any one of Examples
1 through 5, wherein the porous light scattering particles have a
refractive index of greater than or equal to about 2.0 and the
pores have a refractive index of about 1.0.
[0063] Example 7. The light emitting device of any one of Examples
1 through 6, wherein the porous light scattering particles have
transverse sizes of about 0.3 microns to about 10. microns.
[0064] Example 8. The light emitting device of any one of Examples
1 through 7, wherein the porous light scattering particles have a
bimodal size distribution with a first peak at a first transverse
size and a second peak at about one fourth or less of the first
transverse size.
[0065] Example 9. The light emitting device of any one of Examples
1 through 8, wherein the pores have transverse sizes of about 0.10
microns to about 0.50 microns.
[0066] Example 10. The light emitting device of any one of Examples
1 through 9, wherein at least some of the porous light scattering
particles include a hydrophobic coating.
[0067] Example 11. The light emitting device of Example 10, wherein
the hydrophobic coating coats internal surfaces of at least some of
the pores in the porous light scattering particles.
[0068] Example 12. The light emitting device of any one of Examples
1 through 11, wherein: the porous light scattering particles have a
refractive index of greater than or equal to about 2.0; the pores
have a refractive index of about 1.0; and at least some of the
porous light scattering particles include a hydrophobic
coating.
[0069] Example 13. The light emitting device of Example 12, wherein
the porous light scattering particles have diameters of about 0.3
microns to about 10. microns.
[0070] Example 14. The light emitting device of any one of Examples
12 or 13, wherein the pores have transverse sizes of about 0.20
microns to about 0.25 microns.
[0071] Example 15. A light emitting device comprising: a plurality
of phosphor converted light emitting diodes disposed on a shared
substrate with adjacent phosphor converted light emitting diodes
separated by gaps; and a light scattering composition filling the
gaps to form sidewall reflectors shared by adjacent phosphor
converted light emitting diodes, the light scattering composition
comprising porous light scattering particles dispersed in a
transparent binder, the porous light scattering particles each
including one or more pores defined by inner surfaces of the porous
light scattering particles.
[0072] Example 16. The light emitting device of Example 15, wherein
at least some of the porous light scattering particles include
therein one or more gas-filled pores.
[0073] Example 17. The light emitting device of any one of Examples
15 or 16, wherein at least some of the porous light scattering
particles include therein one or more evacuated pores.
[0074] Example 18. The light emitting device of any one of Examples
15 through 17, wherein at least some of the porous light scattering
particles include therein one or more closed pores.
[0075] Example 19. The light emitting device of any one of Examples
15 through 18, wherein at least some of the porous light scattering
particles include therein one or more open pores.
[0076] Example 20. The light emitting device of any one of Examples
15 through 19, wherein the gaps have a width between adjacent
phosphor converted light emitting diodes of less than or equal to
about 50 microns.
[0077] Example 21. The light emitting device of Example 20, wherein
the gaps have a width between adjacent phosphor converted light
emitting diodes of less than or equal to about 15 microns.
[0078] Example 22. The light emitting device of any one of Examples
15 through 21, wherein the porous light scattering particles have a
refractive index of greater than or equal to about 2.0 and the
pores have a refractive index of about 1.0.
[0079] Example 23. The light emitting device of any one of Examples
15 through 22, wherein the porous light scattering particles have
transverse sizes of about 0.3 microns to about 10. microns.
[0080] Example 24. The light emitting device of any one of Examples
15 through 23, wherein the pores have transverse sizes of about
0.10 microns to about 0.50 microns.
[0081] Example 25. The light emitting device of any one of Examples
15 through 24, wherein one or more of the porous light scattering
particles include a hydrophobic coating.
[0082] Example 26. The light emitting device of Example 25, wherein
the hydrophobic coating coats internal surfaces of at least some of
the pores in the porous particle.
[0083] Example 27. The light emitting device of any one of Examples
15 through 26, wherein: the gaps have a width between adjacent
phosphor converted light emitting diodes of less than or equal to
about 50 microns; the porous light scattering particles have a
refractive index of greater than or equal to about 2.0 and
diameters of about 0.3 microns to about 10. microns; the pores have
diameters of about 0.10 microns to about 0.50 microns and a
refractive index of about 1.0; and the porous light scattering
particles each comprise a hydrophobic coating.
[0084] Example 28. The light emitting device of Example 27, wherein
the gaps have a width between adjacent phosphor converted light
emitting diodes of less than or equal to about 15 microns.
[0085] This disclosure is illustrative and not limiting. Further
modifications will be apparent to one skilled in the art in light
of this disclosure and are intended to fall within the scope of the
present disclosure or appended claims. It is intended that
equivalents of the disclosed example embodiments and methods, or
modifications thereof, shall fall within the scope of the present
disclosure or appended claims.
[0086] In the foregoing Detailed Description, various features may
be grouped together in several example embodiments for the purpose
of streamlining the disclosure. This method of disclosure is not to
be interpreted as reflecting an intention that any claimed
embodiment requires more features than are expressly recited in the
corresponding claim. Rather, as the appended claims reflect,
inventive subject matter may lie in less than all features of a
single disclosed example embodiment. Therefore, the present
disclosure shall be construed as implicitly disclosing any
embodiment having any suitable subset of one or more features --
which features are shown, described, or claimed in the present
application -- including those subsets that may not be explicitly
disclosed herein. A "suitable" subset of features includes only
features that are neither incompatible nor mutually exclusive with
respect to any other feature of that subset. Accordingly, the
appended claims are hereby incorporated in their entirety into the
Detailed Description, with each claim standing on its own as a
separate disclosed embodiment. In addition, each of the appended
dependent claims shall be interpreted, only for purposes of
disclosure by said incorporation of the claims into the Detailed
Description, as if written in multiple dependent form and dependent
upon all preceding claims with which it is not inconsistent. It
should be further noted that the cumulative scope of the appended
claims can, but does not necessarily, encompass the whole of the
subject matter disclosed in the present application.
[0087] The following interpretations shall apply for purposes of
the present disclosure and appended claims. The words "comprising,"
"including," "having," and variants thereof, wherever they appear,
shall be construed as open ended terminology, with the same meaning
as if a phrase such as "at least" were appended after each instance
thereof, unless explicitly stated otherwise. The article "a" shall
be interpreted as "one or more" unless "only one," "a single," or
other similar limitation is stated explicitly or is implicit in the
particular context; similarly, the article "the" shall be
interpreted as "one or more of the" unless "only one of the," "a
single one of the," or other similar limitation is stated
explicitly or is implicit in the particular context. The
conjunction "or" is to be construed inclusively unless: (i) it is
explicitly stated otherwise, e.g., by use of "either . . . or,"
"only one of," or similar language; or (ii) two or more of the
listed alternatives are understood or disclosed (implicitly or
explicitly) to be incompatible or mutually exclusive within the
particular context. In that latter case, "or" would be understood
to encompass only those combinations involving
non-mutually-exclusive alternatives. In one example, each of "a dog
or a cat," "one or more of a dog or a cat," and "one or more dogs
or cats" would be interpreted as one or more dogs without any cats,
or one or more cats without any dogs, or one or more of each. In
another example, each of "a dog, a cat, or a mouse," "one or more
of a dog, a cat, or a mouse," and "one or more dogs, cats, or mice"
would be interpreted as (i) one or more dogs without any cats or
mice, (ii) one or more cats without and dogs or mice, (iii) one or
more mice without any dogs or cats, (iv) one or more dogs and one
or more cats without any mice, (v) one or more dogs and one or more
mice without any cats, (vi) one or more cats and one or more mice
without any dogs, or (vii) one or more dogs, one or more cats, and
one or more mice. In another example, each of "two or more of a
dog, a cat, or a mouse" or "two or more dogs, cats, or mice" would
be interpreted as (i) one or more dogs and one or more cats without
any mice, (ii) one or more dogs and one or more mice without any
cats, (iii) one or more cats and one or more mice without and dogs,
or (iv) one or more dogs, one or more cats, and one or more mice;
"three or more," "four or more," and so on would be analogously
interpreted.
[0088] For purposes of the present disclosure or appended claims,
when terms are employed such as "about equal to," "substantially
equal to," "greater than about," "less than about," and so forth,
in relation to a numerical quantity, standard conventions
pertaining to measurement precision and significant digits shall
apply, unless a differing interpretation is explicitly set forth.
For null quantities described by phrases such as "substantially
prevented," "substantially absent," "substantially eliminated,"
"about equal to zero," "negligible," and so forth, each such phrase
shall denote the case wherein the quantity in question has been
reduced or diminished to such an extent that, for practical
purposes in the context of the intended operation or use of the
disclosed or claimed apparatus or method, the overall behavior or
performance of the apparatus or method does not differ from that
which would have occurred had the null quantity in fact been
completely removed, exactly equal to zero, or otherwise exactly
nulled.
[0089] For purposes of the present disclosure and appended claims,
any labelling of elements, steps, limitations, or other portions of
an embodiment, example, or claim (e.g., first, second, third, etc.,
(a), (b), (c), etc., or (i), (ii), (iii), etc.) is only for
purposes of clarity, and shall not be construed as implying any
sort of ordering or precedence of the portions so labelled. If any
such ordering or precedence is intended, it will be explicitly
recited in the embodiment, example, or claim or, in some instances,
it will be implicit or inherent based on the specific content of
the embodiment, example, or claim. In the appended claims, if the
provisions of 35 USC .sctn. 112(f) are desired to be invoked in an
apparatus claim, then the word "means" will appear in that
apparatus claim. If those provisions are desired to be invoked in a
method claim, the words "a step for" will appear in that method
claim. Conversely, if the words "means" or "a step for" do not
appear in a claim, then the provisions of 35 USC .sctn. 112(f) are
not intended to be invoked for that claim.
[0090] If any one or more disclosures are incorporated herein by
reference and such incorporated disclosures conflict in part or
whole with, or differ in scope from, the present disclosure, then
to the extent of conflict, broader disclosure, or broader
definition of terms, the present disclosure controls. If such
incorporated disclosures conflict in part or whole with one
another, then to the extent of conflict, the later-dated disclosure
controls.
[0091] The Abstract is provided as required as an aid to those
searching for specific subject matter within the patent literature.
However, the Abstract is not intended to imply that any elements,
features, or limitations recited therein are necessarily
encompassed by any particular claim. The scope of subject matter
encompassed by each claim shall be determined by the recitation of
only that claim.
* * * * *